1. Field of the Invention
The present invention relates to a transmission system, and particularly, to a transmission system for an audio-video optical wireless transmission apparatus or a wired optical signal transmission apparatus, capable of multiplexing an uncompressed baseband digital HD (high definition) video signal, a digital audio signal, and a digital auxiliary control signal including a video signal format and an audio signal format, serially transmitting the multiplexed signal as an optical signal with an optical wireless transmitter or an optical signal transmission cable, receiving the optical signal, demultiplexing the received signal into the video signal, audio signal, and auxiliary control signal, and regenerating the video and audio signals.
2. Description of Related Art
There are known transmission systems that convert an uncompressed baseband digital HD (high definition) video signal into an optical signal and serially transmit the optical signal. An example of such a system is disclosed in Japanese Unexamined Patent Application Publication No. 2000-209622. A DVI (digital visual interface) standard defines a transmission system for transmitting an uncompressed baseband digital HD video signal through a cable. The DVI standard mainly targets digital video signal transmission with personal computers and is only capable of handling three primary color signals of red(R), green(G), and blue(B). Namely, it requires an audio signal to be transmitted separately. When applied to an AV device, the DVI standard requires the AV device to be connected to an audio cable in addition to a video cable.
To solve the connection problem, there is an HDMI (high-definition multimedia interface) standard developed for the AV field. The HDMI standard can handle a component video signal and can simultaneously transmit an uncompressed audio signal.
FIG. 1 shows a data transmission format employed by the HDMI standard. The HDMI standard transmits a whole video signal 46 that includes blanking periods contained in horizontal and vertical synchronizing signals. Namely, the whole video signal 46 includes an effective video signal area 47 consisting of 720 effective pixels by 480 effective lines and a blanking area 48 consisting of 139 pixels in a horizontal direction and 45 lines in a vertical direction. In the blanking area 48, an audio signal, an auxiliary control signal, and the like are multiplexed and transmitted.
There is another known optical transmission system that transmits compressed video and audio signals. An example thereof is disclosed in Japanese Patent Publication No. 3329927 (the second page). The transmission system disclosed in this publication includes a data transmission apparatus having a transmitter for transmitting supplied video and audio data and a remote receiver for receiving the transmitted data. The transmitter relates the supplied data to preset hierarchical levels and transmits the data by shifting the transmission timing by a predetermined quantity level by level and by overlapping the data. The receiver receives the overlapped data and stores the data in a memory in a hierarchy of compressed data pieces each of a predetermined quantity. Even if a transmission line is disconnected, this related art properly combines the hierarchical data to provide continuous data.
The transmission system of the Japanese Unexamined Patent Application Publication No. 2000-209622 employs, as a data transmission network, a computer network based on IEEE1394 or an asynchronous transfer mode (ATM) network. Namely, this related art is fiber transmission and is inapplicable to space transmission. The DVI standard mentioned above is limited to wired (cable) transmission and needs an audio cable in addition to a video cable when applied to AV devices.
The transmission system of the Japanese Patent Publication No. 3329927 can continue the regeneration of video and audio signals in the event of a transmission line disconnection of a relatively short time by regularly time-compressing K (a real number greater than 1) times as large data as a normal data block to be transmitted without interruption and by intermittently transmitting the compressed data. Namely, to transmit an uncompressed baseband digital HD video signal and a digital audio signal, the related art needs a FIFO whose capacity is K times as large as the normal data block. In addition, the related art needs a transmission clock of, for example, several Gbps that is K times faster than a standard clock. Such a large FIFO and a fast transmission clock are unachievable. If the digital video signal and digital audio signal are compressed according to, for example, MPEG, such a large FIFO and a fast transmission speed will not be needed, and therefore, transmission thereof by the related art will be achievable.
The HDMI standard mentioned above allows a component video signal and an uncompressed audio signal to be simultaneously transmitted. The HDMI standard employs TMDS (transition minimized differential signaling) which is also adopted by the DVI standard. The TMDS employs 3-channel lines to transmit a video signal, an audio signal, and a control signal, as well as blanking signals for vertical and horizontal synchronization. In addition, the TMDS employs a 1-channel line to transmit a clock signal. Namely, the TMDS uses four channels in total to realize high-density, high-speed transmission.
Simply transmitting these signals with the use of an optical wireless transmission apparatus requires four optical wireless transmission lines or an optical multiplexing process. This increases costs and enlarges the apparatus. To realize high-speed transmission with a single light beam and to secure a transmission distance of 10 m or longer as required by the HDMI standard, the power of the light beam must be increased. This also increases costs and enlarges the apparatus.
As explained with reference to FIG. 1, a transmission system employing the HDMI standard entirely transmits horizontal and vertical synchronizing signals including blanking periods. Although the blanking periods are used to transmit audio and control signals, entirely transmitting the blanking periods is wasteful. To secure a transmission distance of 10 m or over in wired transmission, each of the four channels must differentially be driven with two signal lines. Although these signal lines are gathered in a single cable, there is a necessity of conducting troublesome work of wiring them to a display section.